(core) move data engine code to core

Summary:
this moves sandbox/grist to core, and adds a requirements.txt
file for reconstructing the content of sandbox/thirdparty.

Test Plan:
existing tests pass.
Tested core functionality manually.  Tested docker build manually.

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2563

sandbox/gen_js_schema.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python -B
+"""
+Generates a JS schema file from sandbox/grist/schema.py.
+"""
+
+import os
+import sys
+sys.path.append(os.path.join(os.path.dirname(__file__), 'grist'))
+
+import schema   # pylint: disable=import-error,wrong-import-position
+
+# These are the types that appear in Grist metadata columns.
+_ts_types = {
+  "Bool":           "boolean",
+  "DateTime":       "number",
+  "Int":            "number",
+  "PositionNumber": "number",
+  "Ref":            "number",
+  "Text":           "string",
+}
+
+def get_ts_type(col_type):
+  col_type = col_type.split(':', 1)[0]      # Strip suffix for Ref:, DateTime:, etc.
+  return _ts_types.get(col_type, "CellValue")
+
+def main():
+  print """
+/*** THIS FILE IS AUTO-GENERATED BY %s ***/
+// tslint:disable:object-literal-key-quotes
+
+export const schema = {
+""" % __file__
+
+  for table in schema.schema_create_actions():
+    print '  "%s": {' % table.table_id
+    for column in table.columns:
+      print '    %-20s: "%s",' % (column['id'], column['type'])
+    print '  },\n'
+
+  print """};
+
+export interface SchemaTypes {
+"""
+  for table in schema.schema_create_actions():
+    print '  "%s": {' % table.table_id
+    for column in table.columns:
+      print '    %s: %s;' % (column['id'], get_ts_type(column['type']))
+    print '  };\n'
+  print "}"
+
+if __name__ == '__main__':
+  main()